A variable frequency soft switching boost-flyback converter for high step-up applications

This paper proposes a variable frequency zero-voltage-switching (ZVS) digital controlled boost-flyback converter (BFC) to achieve high efficiency and high step-up conversion. With no auxiliary switch introduced, ZVS of the MOSFETs can be achieved and reverse-recovery of diode eliminated naturally by operating the converter in boundary-conduction-mode. With the proposed control, both soft-switching and high efficiency are achieved in a wide load range. To achieve higher step-up ratio, lower voltage and current ripple in both input and output and lower current stress of the switches, a two-channel interleaved parallel-input/series-output BFC is presented. The operation principle and control strategy is analyzed in detail and verified with a 230W 30V to 380V prototype.